Blood found on Sion Jenkins' clothing after the murder of his teenage foster daughter could have got there as he comforted her in her dying moments.

Lawyers acting for the former headteacher, convicted of killing 13-year-old Billie-Jo Jenkins, said forensic evidence used at his first appeal was wrong.

The Court of Appeal in London yesterday heard the rejection of the appeal in 1999 was based on flawed scientific evidence from prosecution pathologist Dr Ian Hill.

Jenkins, 46, looked on intently from behind a steel-barred dock as evidence centred on blockages in Billie-Jo's lungs.

His counsel said a mist of blood found on Jenkins could have been caused by the movement of a blockage in Billie-Jo's lungs, which forced the blood out as he comforted her and not as a result of him killing her.

Dr Hill had successfully argued there was only a blockage in her lower airways but the court heard the blockage was, in fact, in the upper airways.

Under cross-examination from defence counsel Clare Montgomery, QC, Dr Hill said: "That was the only obstruction I found."

The basis of Dr Hill's opinion, as he told the court in 1999, was if there had been a blockage higher up he would have noticed.

Nevertheless, at the appeal the judges rejected lung physiologist Professor David Dennison's theory that a brief passive release of pressure of Billie-Jo's upper airways caused by the movement of the blockage could have resulted in the exhalation of a fine mist of blood.

He argued the mist could have settled on Jenkins' clothes as he tended Billie-Jo after discovering her body following an aborted trip to a DIY store.

Jenkins has been serving life in jail since his conviction at Lewes Crown Court in 1998 for battering Billie-Jo to death.

Jenkins, who was headteacher-designate at William Parker School in Hastings, was said to have bludgeoned Billie-Jo with an 18in metal tent spike as she painted patio doors at the family home in Lower Park Road, Hastings, in February 1997.

Jenkins has always maintained his innocence, insisting he was convicted on false evidence. After the court's rejection of the first appeal, Jenkins instructed two lung experts to examine Dr Hill's opinion.

They examined sections of Billie-Jo's lung tissue, work which Dr Hill never carried out.

The examination suggested any obstruction was present at a higher level in Billy-Jo's airways.

Miss Montgomery suggested to Dr Hill that he gave evidence at the court using "partial information", to which he replied: "If you say so."

However, Dr Hill said although he now accepts there was an upper airway blockage it would not have affected the spray of blood.

Jenkins' defence now believe the court's basis for rejecting Prof Dennison's theory is no longer valid and there is a plausible explanation as to how Jenkins could have received small droplets of Billie-Jo's blood on his clothing.

The hearing continues.